In conventional machine protection and prediction monitoring systems, many different types of sensors are used to measure various properties of a machine, such as eddy current sensors, seismic sensors, passive magnetic sensors, piezo electric sensors, Hall-effect sensors, and low frequency sensors. Each of these sensor types has its unique characteristics related to sensor supply voltages and currents and signal output voltage ranges. To accommodate these many different types of sensors, a large number of different sensor input modules have to be developed, tested and stocked. Separate modules are typically also needed for tachometer inputs. If a single sensor interface module could handle all these various sensors and measurements, project management would be easier, production and procurement would be more cost-effective, and the number of devices in stock and the spare parts needed could be significantly reduced.
Supplying power to a plurality of sensors from a single multichannel vibration acquisition card has historically necessitated cumbersome circuit complexity due to practical application considerations, including:                Avoidance of potential adverse consequences arising from a sensor or wiring fault that results in shorted sensor power, including:                    Damage to the immediate hardware;            Excessive power dissipation causing smoke or fire hazard;            Excessive demand placed upon the singular sensor power supply;            Adverse impact upon healthy adjacent sensor functionality;            Generation of incorrect control or alarm values derived from adversely affected adjacent sensor readings; and            Overall acquisition card failure;                        Avoidance of potential adverse consequences arising from a concurrent plurality of sensor wiring faults, including:                    Adverse impact upon cards adjacent to and upstream from the faulted card;            Excessive demand placed upon the common board-level and the upstream sensor power supplies;            Excessive temperature elevation within the system enclosure; and            Overall acquisition system failure;                        Minimization of adverse data integrity effects in healthy sensor channels arising from the make/break chatter of faulty or loose adjacent sensor wiring connections;        Minimization of adverse data integrity effects in healthy sensor channels arising from the practice of “hot wiring” adjacent sensor connections;        Avoidance of adverse consequences resulting from sensor-terminal miss-wiring, e.g., connecting a +24V output to a −24V output;        Avoidance of adverse consequences resulting from connecting an external DC voltage source to a sensor supply output; and        Minimization of instantaneous energy available for the generation of hazardous sparks (pertinent to safety-critical environments, e.g. Class 1 Division 2).        
The above considerations can present significant challenges to realizing cost-effective and space-constrained implementations of sensor power supply circuitry. There exists a dearth of effective integrated solutions from electronic component manufacturers, possibly due to the uncommon nature of sensor power, i.e., relatively high DC voltage at relatively low current. It is more typical to find integrated solutions for the mirror condition of low voltage and high current.
Hardware implementations of sensor interfaces in the prior art apply various combined techniques to accomplish the overall desired performance goals. These techniques tend to involve high complexity and over-specification of components and power supplies, and are often not congruent with practical space constraints. Fundamentally, a comprehensive sensor supply implementation for a multichannel sensor interface card should:                (1) provide a fast (virtually instantaneous) limiting response to a short-circuit fault;        (2) provide an accurate limiting response to a short-circuit fault;        (3) survive a continuous short-circuit fault;        (4) survive a plurality of concurrent continuous short-circuit faults in congruence with uninterrupted electrical and thermal integrity of the acquisition system;        (5) automatically recover from short circuit faults;        (6) reduce power consumption/dissipation when in a faulted condition;        (7) isolate adverse effects of a faulted channel from uninvolved channels on the same card;        (8) isolate adverse effects of loose wiring termination “chatter” from uninvolved channels on the same card;        (9) protect against adverse effects resulting from the practice of “hot wiring” sensors;        (10) protect the card and the system against reasonably anticipated installation wiring errors; and        (11) minimize the availability of spark-inducing energy to the field wiring.        
Although the sensible application of discrete semiconductors can realize attribute (1) above, the electrical DC parameters of those devices exhibit significant variability, particularly when evaluated over the industrial temperature range. This variability hampers the ability to achieve attribute (2) when using the same circuitry as used to achieve attribute (1). Alternatively, one can readily implement attribute (2) through the use of a common op-amp, with the resulting solution exhibiting a response time that is too slow to achieve attribute (1). It follows that it may be reasonable to combine the op-amp and discrete solutions together in a parallel path, thereby achieving coarse, but nearly instantaneous limiting, that eventually settles into accurate long-term limiting. This approach has been implemented in prior art. However, due to variability of the initial coarse limiting stage, the method is not an optimum approach for realizing attributes (7), (8), (9) and (11) above.
What is desired is a universal sensor interface for a machine protection and prediction monitoring system that includes a sensor power control circuit that adequately achieves all of attributes (1) through (11) listed above.